Regenerated cellulose filaments having high resiliency



United States Patent 3,549,308 REGENERATED CELLULOSE FILAMENTS HAVING HIGH RESILIENCY Mary E. Carter, Philadelphia, Pa., assignor to FMC Corporation, Philadelphia, Pa., a corporation of Delaware No Drawing. Filed Dec. 7, 1966, Ser. No. 601,287 Int. Cl. D06m 13/12, 13/34 US. Cl. 8-1163 Claims ABSTRACT OF THE DISCLOSURE Stretch oriented, wet-gel rayon filaments having a skincore structure, are treated with a cross-linking agent and cured to improve resiliency.

Rayon yarn has poor work recovery or resiliency. This property can be improved by chemical cross-linking, but because of the difference in fine structure of various rayons, they respond differently to chemical modification.

It is desirable that rayon having a work'recovery equal to or approaching synthetic thermoplastic fibers be developed for use in carpet and various other textile applications. This is accomplished in accordance with the present invention, generally speaking, by chemical modification of a specified type of regenerated cellulose fiber in a specified state.

The prior art has shown the treatment of wet-gel rayon with cross-linking agents to modify fiber characteristics. However, the increase in work recovery necessary to provide a fiber or yarn equivalent to or approaching synthetic thermoplastic fibers, has not been fully realized by prior workers in this field, and this is a primary object of this invention.

The present invention accomplishes the above objective in a method comprising treating wet-gel rayon filaments having a skin-core cross-sectional structure of from about 5 to less than 50% skin, said filaments having been stretch oriented no more than 50% of their original length, with an aqueous medium containing a compound capable of causing the cellulose molecules to cross-link, drying the filaments and curing.

The critical features of this invention are the combination of a Wet-gel filament, a specific fine structure of the rayon and, of course, the treatment of the rayon in this condition with a compound which will cause crosslinking.

Wet-gel rayon is also termed never-dried rayon. In this condition, the cellulose structure is fully open and has a much greater tendency to receive the cross-linking reagent than a fiber which has been collapsed by drying and then rewet.

The fine structure of the regenerated cellulose has been discussed in the literature, for example, see The Spinning of Rayon as Related to Its Structure and Properties, by Wayne A. Sisson, Textile Research Journal, vol. 30, March 1960. The fine structure of the filament includes its crystallinity (lateral order) and orientation.

In considering crystallinity, one must take into account the degree of crystalline-like structure as opposed to amorphous-like structure, as well as the size and distribution of the crystallites in the filaments. These characteristics are determined primarily by the consistency of the viscose and the spinning bath in the formation of fibers in a viscose system. For example, fibers which are either all core, oil skin, thick skin, or thin skin are obtained by varying the spinning conditions.

Orientation is the forced positioning of the molecules in the filament structure generally in alignment with the "ice length of the filament. This is usually accomplished by stretching the fiber under given conditions.

The manufacture of rayon which is particularly useful for the preparation of textile products does not necessarily provide a filament having a fine structure which is useful for the degree of cross-linking necessary for greatly improved resiliency. It has now been found that filaments which have a skin-core structure of a specified proportion or condition and have been stretch oriented, but less than 50% and preferably between about 5 and 25% of their formed length, have an excellent fine structure in the wet-gel state for the purpose of cross-linking and ultimately for obtaining rayon fibers of unexpectedly high resiliency.

The skin-core structure for the rayon of this invention is one wherein the cross-sectional area of the filament is from about 5 to less than 50% skin.

Skin-core structure for regenerated cellulose filaments is generally obtained in the viscose spinning process by extrusion of the viscose into an acid bath containing a small percentage of a metal salt, preferably a zinc salt, which quickly forms an insoluble compound with the cellulose xanthate of the viscose. This compound formation first takes place on the outside of the filament while the interior is still liquid. The thickness of the skin is determined by how far the metal salt penetrates into the viscose filament before the xanthate groups are split off by the acid in the spinning bath. This mechanism is wellknown to those skilled in this art. It is also known to form filaments having a skin which is broken, split or ruptured during its formation. This type of skin is also included in this invention.

The term skin is employed to designate that portion of the regenerated cellulose filaments which is permanently stained or dyed by the following procedure: A microtome section of one or more filaments mounted in a wax block is taken and mounted on a glass slide with Meyers albumin fixative. After dewaxing in xylene, the section is placed in successive baths of 60 percent and 30 percent alcohol for a few minutes each, and it is then stained in 2 percent aqueous solution of Victoria Blue BS cone. (General Dyestuffs Corp.) for one to two hours. At this point, the entire section is blue. By rinsing the section first in distilled water and then in one or more baths composed of 10 percent water and percent dioxane for a period varying from five to thirty minutes, depending on the particular filament, the dye is entirely removed from the core, leaving it restricted to the skin area.

The stretch orientation of the filaments is carried out at any stage during their preparation that is practical. For example, after coagulation, but before complete regeneration; after regeneration is complete, or partially before and partially after. Stretching is accomplished in one or more stages, but the total stretch is no more than 50%, and the fiber must remain in the wet-gel state.

Orientation of the regenerated cellulose filaments is necessary to provide fibers having improved tenacity. Modification of the fine structure by orientation is controlled, for the purposes of this invention, by confining the stretch orientation to no more than 50% and preferably between 5 and 25% of the original filaments. This controlled orientation contributes to the type of fine structure required for penetration of the crosslinking agent.

The type of cross-linking agent used for this invention is not critical, as long as it is capable of effecting chemical cross-linkages between the cellulose chains. A preferred material for this purpose is a metholated nitrogen compound. Metholated nitrogen compounds include, for example, methylol derivatives of triazines, triazones,

hydantoins, ureas, ethylene ureas, urons, carbamates and the like. These compounds and their derivatives in the methylolated state are useful in mixtures as well as in the pure state, and their use as cross-linking agents is well-known in the art.

Other. cross-linking agents include compounds having one or more epoxide groups, e.g. diglycidal ether of diethylene glycol, diglycidal ether of bisphenol A, etc.; compounds having one or more epoxy groups replaced with halohydrin, e.g. chlorohydrin, etc.; compounds containinghalogen groups as well as epoxy groups e.g., epichlorohydrins, etc.; divinyl sulfone, divinyl sulfoxide, divinyl ketone and the like.

The cross-linking agents are used to treat the wet-gel regenerated cellulose filaments incorporated in aqueous mediums at concentrations broadly ranging from about to 50%, preferably from to 25%, based on the weight of the aqueous medium.

Suitable acid or alkaline catalysts or curing accelerators are generally added to the aqueous cross-linking medium before treatment of the filaments although these agents may be applied separately. Acid catalyzed crosslinking agents, e.g., metholated nitrogen compounds, require strong mineral acids, strong organic acids or acid salts including, for example, sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, trichloroacetic acid, acetic acid, zinc nitrate, magnesium nitrate, calcium nitrate, zinc chloride, aluminum chloride, magnesium chloride, and the like.

Base catalyzed cross-linking agents, e.g. divinyl sulfone, require strong basesor basic salts, including, for example, alkali metal hydroxides, sodium sulfide, sodium silicate, tetramethyl ammonium hydroxide and the like.

The concentration of the catalysts in an aqueous medium will depend on the catalyst, the cross-linking agent and conditions employed, but generally the amount will be no more than 50%, based on the weight of the crosslinking agent.

Plasticizing agents for the rayon filaments may be used if desired. These agents may be incorporated in regenerating, stretching, finish or cross-linking baths, as well as separately applied from aqueous mediums containing up to 25% by weight of the plasticizer or swelling agent. Materials for this purpose include, for example, dimethyl sulfoxide, ethylene glycol, dimethyl formamide, and the like. If a plasticizer is used, dimethyl sulfoxide is preferred for this invention.

Other materials, such as finishing agents and cementation reducing agents in conventional amounts, may also be applied during or after the formation of the filaments.

After application of cross-linking agents and other materials from aqueous media, the impregnated regenerated cellulose filaments must be dried. The drying temperature is not critical, except that it should be less than 100 C. Before drying, the filaments are usually squeezed to remove excessive amounts of liquid and then subjected to heat in a drying oven or chamber for from about 5 to 60 minutes. 1

After drying, the filaments are cured. This is advantageously carried out by heating the filaments at a temperature in the range of at least 100 C. up to 200 C. for from 3 to 30 minutes. Higher temperatures which do not degrade the filaments may be used if desired.

The following example is set forth to demonstrate this invention.

EXAMPLE Regenerated cellulose filaments were prepared by spinning a viscose containing 9.0 weight percent cellulose, 6.0 weight percent sodium hydroxide and 23 percent carbon disulfide, based on the weight of the cellulose and having a common salt test of 3 into an aqueous spinning bath containing 5.6 weight percent sulfuric acid, 0.3 weight percent zinc sulfate and 21 weight percent of sodium sulfate, kept at about 53 C. The filaments were spunat a speed of 45 meters per minute and traveled 30 inches through the spinning bath. On leaving the bath, the filaments were stretched in air between two godets, and dropped into a water sluice box having a water inlet temperature of C. The wet-gel filaments from the sluice box were placed into an aqueous bath containing 18% by weight of a methylol derivative of mixed alkyl triazines (Aerotex 23 Special, marketed by American Cyanamid Co.) and 2% by weight of zinc nitrate for 15 minutes. After this, the filaments were spread out in web form, squeezed to pick-up, dried in an oven at 70 C. for 20 minutes, and cured by heating in an oven at C. for 15 minutes. Filaments were spun under the above conditions with stretch orientation ranging from 10 to 45%. The filaments had skin-core structures of less than 50% skin.

The work recovery of these filaments increased to be tween 72 and 89% along with a very high increase in conditioned and. wet tenacity. Work recovery correlates well with actual resiliency and represents the ratio of re- "coverable work-to the total work required to strain a 'rate. The work recovery for the above filaments in fiber form is equal to commercially available acrylic carpet fiber and is anunexpected advancement in the regenerated cellulose fiber art.

Various changes and modifications may be made practicing the invention without departing from the spirit and scope thereof, and therefore, the invention is not to be limited except as defined in the appended claims.

I claim:

1. Cross-linked, regenerated cellulose filaments manufactured from viscose and having improved resiliency prepared by the method which comprises treating wet-gel, oriented regenerated cellulose filaments having a skincore cross sectional structure of from about 5 to less than 50% skin, said filaments having been stretch oriented to between about 5 and about 25% of their original length, with an aqueous medium containing from about .5 to 50% of a compound capable of causing cross-linking of the cellulose molecules in the regenerated cellulose filaments, drying the filaments at a temperature less than 100 C. for from about 5 to 60 minutes, and curing at a temperature between 100 and 200 C. for from 3 to 30 minutes.

2. The filaments of claim 1 .wherein the compound capable of causing cross-linking is a methylolated nitrogen compound.

3. The filaments of claim 1 wherein the wet-gel filaments are also treated with a curing accelerator in an aqueous medium.

4. The filaments of claim 1 wherein the wet-gel filaments have been plasticized.

5. The filaments of claim 1 wherein the compound capable of causing cross-linking is a methylol derivative of an alkyl triazine, and the aqueous medium also contains zinc nitrate in an amount sufiicient to accelerate curing.

References Cited UNITED STATES PATENTS 2,732,279 1/ 1956 Tachikawa 8-116 3,128,147 4/1964 Kenyon et al. 8l16 3,173,752 3/1965 Rowell et a1 8-116 US. Cl. X.R. 8-120; 260-212 1 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,549,308 Dated kw"; 2

Inventofls) Carter, Mary E.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 68, "oil" should read "all" S Am Mil-MI mm 1;. it: .m. m offi )mnmssionea- 01' Patent:

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